 
wherein R1 is hydrogen or a lower alkyl radical and n is 4, 5, or 6 are known in U.S. Pat. No. 4,024,175 and its divisional U.S. Pat. No. 4,087,544. The uses disclosed are: protective effect against cramp induced by thiosemicarbazide; protective action against cardiazole cramp; the cerebral diseases, epilepsy, faintness attacks, hypokinesia, and cranial traumas; and improvement in cerebral functions. The compounds are useful in geriatric patients. The patents are hereby incorporated by reference.
The instant invention is a compound of Formula I and II 
wherein A, X, Y, Z, W, and n are as described below.
The compounds of the invention and their pharmaceutically acceptable salts and the prodrugs of the compounds, are useful in the treatment of epilepsy, faintness attacks, hypokinesia, cranial disorders, neurodegenerative disorders, depression, anxiety, panic, pain, neuropathological disorders, gastrointestinal disorders such as irritable bowel syndrome (IBS), and inflammation, especially arthritis.
The invention is also a pharmaceutical composition of a compound of Formula I or II.
The invention also includes novel intermediates useful in the preparation of the final products.
The compounds of the invention are those of Formula I and II 
or a pharmaceutically acceptable salt thereof wherein:
In Formula I, A is O, S, or NR wherein R is hydrogen, straight or branched alkyl of from 1 to 6 carbon atoms, cycloalkyl of from 3 to 8 carbon atoms, phenyl or benzyl;
In Formula II, A is N;
X, Y, Z and W are each independently hydrogen, straight or branched alkyl of from 1 to 6 carbon atoms;
cycloalkyl of from 3 to 8 carbon atoms, alkoxy, phenyl, benzyl, or halogen; and
n is an integer of from 1 to 4.
Preferred compounds are those of Formula I and II wherein Formula I and II are 
Other preferred compounds are those of Formula I wherein A is oxygen.
Other preferred compounds are those of Formula I wherein A is sulfur.
Other preferred compounds are those of Formula I wherein A is NR.
When A is N, preferred compounds can also be those of Formula II.
More preferred compounds are selected from:
3-Aminomethyl-4-thiophen-2-yl-butyric acid;
3-Aminomethyl-4-thiophen-3-yl-butyric acid;
3-Aminomethyl-4-furan-2-yl-butyric acid;
3-Aminomethyl-4-furan-3-yl-butyric acid;
3-Aminomethyl-4-pyrrole-2-yl-butyric acid;
3-Aminomethyl-4-pyrrole-3-yl-butyric acid; and
3-Aminomethyl-4-pyrrole-1-yl-butyric acid;
The term lower alkyl is a straight or branched group of from 1 to 6 carbons including but not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, except as where otherwise stated.
The benzyl and phenyl groups may be unsubstituted or substituted by from 1 to 3 substituents selected from hydroxy, carboxy, carboalkoxy, halogen, CF3, nitro, alkyl, and alkoxy. Preferred are alkyl
Cycloalkyl is cyclic carbon group of from 3 to 8 atoms.
Alkoxy is a straight or branched group of from 1 to 4 carbons attached to the remainder of the molecule by an oxygen.
Halogen is chlorine, fluorine, bromine, or iodine.
The prodrugs of the compounds include, but are not limited to esters, amides, and carbamates.
Since amino acids are amphoteric, pharmacologically compatible salts of appropriate inorganic or organic acids, for example, hydrochloric, sulphuric, phosphoric, acetic, oxalic, lactic, citric, malic, salicylic, malonic, maleic, succinic, methanesulfonic acid, and ascorbic. Starting from corresponding hydroxides or carbonates, salts with alkali metals or alkaline earth metals, for example, sodium, potassium, magnesium, or calcium are formed. Salts with quaternary ammonium ions can also be prepared with, for example, the tetramethyl-ammonium ion. The carboxyl group of the amino acids can be esterfied by known means.
Certain of the compounds of the present invention can exist in unsolvated forms as well as solvated forms, including hydrated forms. In general, the solvated forms, including hydrated forms, are equivalent to unsolvated forms and are intended to be encompassed within the scope of the present invention.
Certain of the compounds of the present invention possess one or more chiral centers and each center may exist in the R(D) or S(L) configuration. The present invention includes all enantiomeric and epimeric forms as well as the appropriate mixtures thereof.
Animals
Male Sprague-Dawley rats (180-250 g) were obtained from Bantin and Kingman, (Hull, U.K.). Animals were housed in groups of 6 to 10 under a 12 hour light/dark cycle (lights on at 7 hours, 0 minutes) with food and water ad libitum.
Carrageenan-induced Thermal Hyperalgesia in the Rat
Thermal hyperalgesia was assessed using the rat plantar test (Ugo Basile, Italy) following a modified method of Hargreaves, et al., 1988. Rats were habituated to the apparatus which consisted of three individual perspex boxes on an elevated glass table. A mobile radiant heat source located under the table was focused onto the desired paw and paw withdrawal latencies (PWL) recorded. PWL were taken 3 times for both hind paws of each animal, the mean of which represented baselines for right and left hind paws. At least 5 minutes were allowed between each PWL for an animal. The apparatus was calibrated to give a PWL of approximately 10 seconds. There was an automatic cutoff point of 20 seconds to prevent tissue damage. After baseline PWLs were determined, animals received an intraplantar injection of carrageenan (100 xcexcL of 20 mg/mL) into the right hind paw. PWLs were reassessed following the same protocol as above 2-hour post-carrageenan (this time point represented the start of peak hyperalgesia) to ascertain that hyperalgesia had developed. Test compounds were administered orally (in a volume of 1 mL/kg) at 2.5 hours after carrageenan. PWLs were reassessed at various times after drug administration.
A Model of Anticonvulsant Efficacy and Protocol for DBA2 Test: Prevention of Audiogenic Seizures in DBA/2 Mice
Methods
All procedures were carried out in compliance with the NIH Guide for the Care and Use of Laboratory Animals under a protocol approved by the Parke-Davis Animal Use Committee. Male DBA/2 mice, 3 to 4 weeks old, were obtained from Jackson Laboratories, Bar Harbour, Me. Immediately before anticonvulsant testing, mice were placed upon a wire mesh, 4 inches square suspended from a steel rod. The square was slowly inverted through 180 degrees and mice observed for 30 seconds. Any mouse falling from the wire mesh was scored as ataxic.
Mice were placed into an enclosed acrylic plastic chamber (21 cm height, approximately 30 cm diameter) with a high-frequency speaker (4 cm diameter) in the center of the top lid. An audio signal generator (Protek model B-180) was used to produce a continuous sinusoidal tone that was swept linearly in frequency between 8 kHz and 16 kHz once each 10 msec. The average sound pressure level (SPL) during stimulation was approximately 100 dB at the floor of the chamber. Mice were placed within the chamber and allowed to acclimatize for 1 minute. DBA/2 mice in the vehicle-treated group responded to the sound stimulus (applied until tonic extension occurred, or for a maximum of 60 seconds) with a characteristic seizure sequence consisting of wild running followed by clonic seizures, and later by tonic extension, and finally by respiratory arrest and death in 80% or more of the mice. In vehicle-treated mice, the entire sequence of seizures to respiratory arrest lasts approximately 15 to 20 seconds.
The incidence of all the seizure phases in the drug-treated and vehicle-treated mice was recorded, and the occurrence of tonic seizures were used for calculating anticonvulsant ED50 values by probit analysis. Mice were used only once for testing at each dose point. Groups of DBA/2 mice (n=5-10 per dose) were tested for sound-induced seizure responses 2 hours (previously determined time of peak effect) after given drug orally. All drugs in the present study were dissolved in distilled water and given by oral gavage in a volume of 10 mL/kg of body weight. compounds that are insoluble will be suspended in 1% carboxymethocellulose. Doses are expressed as weight of the active drug moiety.
Results
The dose-dependent suppression of sound-induced tonic seizures in DBA/2 mice was tested, and the corresponding ED50 values are shown in Table 1.
The present results show that the compounds of the invention given orally cause dose-related anticonvulsant effects in a sound susceptible strain (DBA/2) of mice, confirming previous data showing anticonvulsant activity in other models of experimental epilepsy. The effective dosages of drugs in this model are lower than those in the maximal electroshock test, confirming that DBA/2 mice are a sensitive model for detecting anticonvulsant actions.
The radioligand binding assay using [3H]gabapentin and the xcex12xcex4 subunit derived from porcine brain tissue was used (xe2x80x9cNovel Anti-convulsant Drug, Gabapentin Binds to the xcex12xcex4 Subunit of a Calcium Channelxe2x80x9d, Gee N. et al., J. Biological Chemistry, in press).
The compounds of the invention show good binding affinity to the xcex12xcex4 subunit. Gabapentin (Neurontin(copyright)) is about 0.10 to 0.12 xcexcM in this assay. Since the compounds of the instant invention also bind to the subunit, they are expected to exhibit pharmacologic properties comparable to gabapentin. For example, as agents for convulsions, anxiety, and pain.
The compounds of the invention are related to Neurontin(copyright), a marketed drug effective in the treatment of epilepsy. Neurontin(copyright) is 1-(aminomethyl)-cyclohexaneacetic acid of structural formula 
The compounds of the invention are also expected to be useful in the treatment of epilepsy.
The present invention also relates to therapeutic use of the compounds of the minetic as agents for neurodegenerative disorders.
Such neurodegenerative disorders are, for example, Alzheimer""s disease, Huntington""s disease, Parkinson""s disease, and Amyotrophic Lateral Sclerosis.
The present invention also covers treating neurodegenerative disorders termed acute brain injury. These include but are not limited to: stroke, head trauma, and asphyxia.
Stroke refers to a cerebral vascular disease and may also be referred to as a cerebral vascular incident (CVA) and includes acute thromboembolic stroke. Stroke includes both focal and global ischemia. Also, included are transient cerebral ischemic attacks and other cerebral vascular problems accompanied by cerebral ischemia such as in a patient undergoing carotid endarterectomy specifically or other cerebrovascular or vascular surgical procedures in general, or diagnostic vascular procedures including cerebral angiography and the like.
Other incidents are head trauma, spinal cord trauma, or injury from general anoxia, hypoxia, hypoglycemia, hypotension as well as similar injuries seen during procedures from embole, hyperfusion, and hypoxia.
The instant invention would be useful in a range of incidents, for example, during cardiac bypass surgery, in incidents of intracranial hemorrhage, in perinatal asphyxia, in cardiac arest, and status epilepticus.
A skilled physician will be able to determine the appropriate situation in which subjects are susceptible to or at risk of, for example, stroke as well as suffering from stroke for administration by methods of the present invention.
The compounds of the invention are also expected to be useful in the treatment of depression. Depression can be the result of organic disease, secondary to stress associated with personal loss, or idiopathic in origin. There is a strong tendency for familial occurrence of some forms of depression suggesting a mechanistic cause for at least some forms of depression. The diagnosis of depression is made primarily by quantification of alterations in patients"" mood. These evaluations of mood are generally performed by a physician or quantified by a neuropsychologist using validated rating scales, such as the Hamilton Depression Rating Scale or the Brief Psychiatric Rating Scale. Numerous other scales have been developed to quantify and measure the degree of mood alterations in patients with depression, such as insomnia, difficulty with concentration, lack of energy, feelings of worthlessness, and guilt. The standards for diagnosis of depression as well as all psychiatric diagnoses are collected in the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) referred to as the DSM-IV-R manual published by the American Psychiatric Association, 1994.
GABA is an inhibitory neurotransmitter with the central nervous system. Within the general context of inhibition, it seems that GABA-mimetics will decrease or inhibit cerebral function and will therefore slow function and decrease mood leading to depression
The compounds of the instant invention may produce an anticonvulsant effect through the increase of newly created GABA at the synaptic junction. If gabapentin does indeed increase GABA levels or the effectiveness of GABA at the synaptic junction, then it could be classified as a GABA-mimetic and might decrease or inhibit cerebral function and might, therefore, slow function and decrease mood leading to depression.
The fact that a GABA agonist or GABA-mimetic might work just the opposite way by increasing mood and thus, be an antidepressant, is a new concept, different from the prevailing opinion of GABA activity heretofore.
The compounds of the instant invention are also expected to be useful in the treatment of anxiety and of panic as demonstrated by means of standard pharmacological procedures.
Carrageenin-Induced Hyperalgesia Another Method
Nociceptive pressure thresholds were measured in the rat paw pressure test using an analgesymeter (Randall-Sellitto Method: Randall L. O., Sellitto J. J., A method for measurement of analgesic activity on inflamed tissue. Arch. Int. Pharmacodyn., 1957;4:409-419). Male Sprague-Dawley rats (70-90 g) were trained on this apparatus before the test day. Pressure was gradually applied to the hind paw of each rat and nociceptive thresholds were determined as the pressure (g) required to elicit paw withdrawal. A cutoff point of 250 g was used to prevent any tissue damage to the paw. On the test day, two to three baseline measurements were taken before animals were administered 100 xcexcL of 2% carrageenin by intraplantar injection into the right hind paw. Nociceptive thresholds were taken again 3 hours after carrageenin to establish that animals were exhibiting hyperalgesia. Animals were dosed with either gabapentin (3-300 mg/kg, s.c.), morphine (3 mg/kg, s.c.), or saline at 3.5 hours after carrageenin and nociceptive thresholds were examined at 4, 4.5, and 5 hours post-carrageenin.
Semicarbazide-Induced Tonic Seizures
Tonic seizures in mice are induced by subcutaneous administration of semicarbazide (750 mg/kg. The latency to the tonic extension of forepaws is noted. Any mice not convulsing within 2.0 hours after semicarbazide are considered protected and given a maximum latency score of 120 minutes.
Animals
Male Hooded Lister rats (200-250 g) are obtained from Interfauna (Huntingdon, UK) and male TO mice (20-25 g) are obtained from Bantin and Kingman (Hull, UK). Both rodent species are housed in groups of six. Ten Common Marmosets (Callithrix Jacchus) weighing between 280 and 360 g, bred at Manchester University Medical School (Manchester, UK) are housed in pairs. All animals are housed under a 12-hour light/dark cycle (lights on at 07.00 hour) and with food and water ad libitum.
Drug Administration
Drugs are administered either intraperitoneally (IP) or subcutaneously (SC) 40 minutes before the test in a volume of 1 mL/kg for rats and marmosets and 10 mL/kg for mice.
Mouse Light/Dark Box
The apparatus is an open-topped box, 45 cm long, 27 cm wide, and 27 cm high, divided into a small (2/5) and a large (3/5) area by a partition that extended 20 cm above the walls (Costall B., et al., Exploration of mice in a black and white box: validation as a model of anxiety. Pharmacol. Biochem. Behav., 1989;32:777-785).
There is a 7.5xc3x977.5 cm opening in the center of the partition at floor level. The small compartment is painted black and the large compartment white. The white compartment is illuminated by a 60-W tungsten bulb. The laboratory is illuminated by red light. Each mouse is tested by placing it in the center of the white area and allowing it to explore the novel environment for 5 minutes. The time spent in the illuminated side is measured (Kilfoil T., et al., Effects of anxiolytic and anxiogenic drugs on exploratory activity in a simple model of anxiety in mice. Neuropharmacol., 1989;28:901-905).
Rat Elevated X-Maze
A standard elevated X-maze (Handley S. L., et al., Effects of alpha-adrenoceptor agonists and antagonists in a maze-exploration model of xe2x80x98fearxe2x80x99-motivated behavior. Naunyn-Schiedeberg""s Arch. Pharmacol., 1984;327:1-5) was automated as previously described (Field, et al., Automation of the rat elevated X-maze test of anxiety. Br. J. Pharmacol., 1991;102(Suppl):304P). The animals are placed on the center of the X-maze facing one of the open arms. For determining anxiolytic effects the entries and time spent on the end half sections of the open arms is measured during the 5-minute test period (Costall, et al., Use of the elevated plus maze to assess anxiolytic potential in the rat. Br. J. Pharmacol., 1989,96(Suppl):312P).
Marmoset Human Threat Test
The total number of body postures exhibited by the animal towards the threat stimulus (a human standing approximately 0.5 m away from the marmoset cage and staring into the eyes of the marmoset) is recorded during the 2-minute test period. The body postures scored are slit stares, tail postures, scent marking of the cage/perches, piloerection, retreats, and arching of the back. Each animal is exposed to the threat stimulus twice on the test day before and after drug treatment. The difference between the two scores is analyzed using one-way analysis of variance followed by Dunnett""s t-test. All drug treatments are carried out SC at least 2 hours after the first (control) threat. The pretreatment time for each compound is 40 minutes.
Rat Conflict Test
Rats are trained to press levers for food reward in operant chambers. The schedule consists of alternations of four 4-minute unpunished periods on variable interval of 30 seconds signaled by chamber lights on and three 3-minute punished periods on fixed ratio 5 (by footshock concomitant to food delivery) signaled by chamber lights off. The degree of footshock is adjusted for each rat to obtain approximately 80% to 90% suppression of responding in comparison with unpunished responding. Rats receive saline vehicle on training days.
The compounds of the instant invention are also expected to be useful in the treatment of pain and phobic disorders (Am. J. Pain Manag., 1995;5:7-9).
The compounds of the instant invention are also expected to be useful in treating the symptoms of manic, acute or chronic, single upside, or recurring. They are also expected to be useful in treating and/or preventing bipolar disorder (U.S. Pat. No. 5,510,381).
Models of Irritable Bowel Syndrome
TNBS-Induced Chronic Visceral Allodynia In Rats
Injections of trinitrobenzene sulfonic (TNBS) into the colon have been found to induce chronic colitis. In human, digestive disorders are often associated with visceral pair. In these pathologies, the visceral pain threshold is decreased indicating a visceral hypersensitivity. Consequently, this study was designed to evaluate the effect of injection of TNBS into the colon on visceral pain threshold in a experimental model of colonic distension.
Materials and Methods
Animal and surgery
Male Sprague-Dawley rats (Janvier, Le Genest-St-Ilse, France) weighing 340-400 g are used. The animals are housed 3 per cage in a regulated environment (20xc2x11xc2x0 C., 50xc2x15% humidity, with light 8:00 am to 8:00 pm). Under anesthesia (ketamine 80 mg/kg i.p; acepromazin 12 mg/kg ip), the injection of TNBS (50 mg/kg) or saline (1.5 mL/kg) is performed into the proximal colon (1 cm from the cecum). After the surgery, animals are individually housed in polypropylene cages and kept in a regulated environment (20xc2x11xc2x0 C., 50xc2x15% humidity, with light 8:00 AM to 8:00 PM during 7 days.
Experimental Procedure
At Day 7 after TNBS administration, a balloon (5-6 cm length) is inserted by anus and kept in position (tip of balloon 5 cm from the anus) by taping the catheter to the base of the tail. The balloon is progressively inflated by step of 5 mm Hg, from 0 to 75 mm Hg, each step of inflation lasting 30 seconds. Each cycle of colonic distension is controlled by a standard barostat (ABS, St-Dixc3xa9, France). The threshold corresponds to the pressure which produced the first abdominal contraction and the cycle of distension is then discontinued. The colonic threshold (pressure expressed in mm Hg) is determined after performance of four cycles of distension on the same animal.
Determination of the Activity of the Compound
Data is analyzed by comparing test compound-treated group with TNBS-treated group and control group. Mean and sem are calculated for each group. The antiallodynic activity of the compound is calculated as follows:
Activity (%)=(group Cxe2x88x92group T)/(group Axe2x88x92group T)
Group C: mean of the colonic threshold in the control group
Group T: mean of the colonic threshold in the TNBS-treated group
Group A: mean of the colonic threshold in the test compound-treated group
Statistical Analysis
Statistical significance between each group was determined by using a one-way ANOVA followed by Student""s unpaired t-test. Differences were considered statistically significant at p less than 0.05.
Compounds
TNBS is dissolved in EtOH 30% and injected under a volume of 0.5 mL/rat. TNBS is purchased from Fluka.
Oral administration of the test compound or its vehicle is performed 1 hour before the colonic distension cycle.
The compounds of the present invention can be prepared and administered in a wide variety of oral and parenteral dosage forms. Thus, the compounds of the present invention can be administered by injection, that is, intravenously, intramuscularly, intracutaneously, subcutaneously, intraduodenally, or intraperitoneally. Also, the compounds of the present invention can be administered by inhalation, for example, intranasally. Additionally, the compounds of the present invention can be administered transdermally. It will be obvious to those skilled in the art that the following dosage forms may comprise as the active component, either a compound of Formula I or II or a corresponding pharmaceutically acceptable salt of a compound of Formula I or II.
For preparing pharmaceutical compositions from the compounds of the present invention, pharmaceutically acceptable carriers can be either solid or liquid. Solid form preparations include powders, tablets, pills, capsules, cachets, suppositories, and dispersible granules. A solid carrier can be one or more substances which may also act as diluents, flavoring agents, binders, preservatives, tablet disintegrating agents, or an encapsulating material.
In powders, the carrier is a finely divided solid which is in a mixture with the finely divided active component.
In tablets, the active component is mixed with the carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired.
The powders and tablets preferably contain from five or ten to about seventy percent of the active compound. Suitable carriers are magnesium carbonate, magnesium stearate, talc, sugar, lactose, pectin, dextrin, starch, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose, a low melting wax, cocoa butter, and the like. The term xe2x80x9cpreparationxe2x80x9d is intended to include the formulation of the active compound with encapsulating material as a carrier providing a capsule in which the active component with or without other carriers, is surrounded by a carrier, which is thus in association with it. Similarly, cachets and lozenges are included. Tablets, powders, capsules, pills, cachets, and lozenges can be used as solid dosage forms suitable for oral administration.
For preparing suppositories, a low melting wax, such as a mixture of fatty acid glycerides or cocoa butter, is first melted, and the active component is dispersed homogeneously therein, as by stirring. The molten homogenous mixture is then poured into convenient sized molds, allowed to cool, and thereby to solidify.
Liquid form preparations include solutions, suspensions, and emulsions, for example, water or water propylene glycol solutions. For parenteral injection liquid preparations can be formulated in solution in aqueous polyethylene glycol solution.
Aqueous solutions suitable for oral use can be prepared by dissolving the active component in water and adding suitable colorants, flavors, stabilizing and thickening agents as desired.
Aqueous suspensions suitable for oral use can be made by dispersing the finely divided active component in water with viscous material, such as natural or synthetic gums, resins, methylcellulose, sodium carboxymethylcellulose, and other well-known suspending agents.
Also included are solid form preparations which are intended to be converted, shortly before use, to liquid form preparations for oral administration. Such liquid forms include solutions, suspensions, and emulsions. These preparations may contain, in addition to the active component, colorants, flavors, stabilizers, buffers, artificial and natural sweeteners, dispersants, thickeners, solubilizing agents, and the like.
The pharmaceutical preparation is preferably in unit dosage form. In such form the preparation is subdivided into unit doses containing appropriate quantities of the active component. The unit dosage form can be a packaged preparation, the package containing discrete quantities of preparation, such as packeted tablets, capsules, and powders in vials or ampoules. Also, the unit dosage form can be a capsule, tablet, cachet, or lozenge itself, or it can be the appropriate number of any of these in packaged form.
The quantity of active component in a unit dose preparation may be varied or adjusted from 0.1 mg to 1 g according to the particular application and the potency of the active component. In medical use the drug may be administered three times daily as, for example, capsules of 100 or 300 mg. The composition can, if desired, also contain other compatible therapeutic agents.
In therapeutic use, the compounds utilized in the pharmaceutical method of this invention are administered at the initial dosage of about 0.01 mg to about 100 mg/kg daily. A daily dose range of about 0.01 mg to about 100 mg/kg is preferred. The dosages, however, may be varied depending upon the requirements of the patient, the severity of the condition being treated, and the compound being employed. Determination of the proper dosage for a particular situation is within the skill of the art. Generally, treatment is initiated with smaller dosages which are less than the optimum dose of the compound. Thereafter, the dosage is increased by small increments until the optimum effect under the circumstances is reached. For convenience, the total daily dosage may be divided and administered in portions during the day, if desired.
General Synthetic Routes 
The ester 1 can be prepared by heating to reflux of the corresponding acid in a solvent such as ethanol and the like in the presence of a catalytic amount of mineral acid such as hydrochloric acid. It can also be prepared from the acid with an appropriate chloroformate in the presence of DMAP and a base such as triethylamine. Alternatively, the ester can also be prepared from the corresponding aldehyde via a xe2x80x9cWittig-likexe2x80x9d reaction followed by hydrogenation of the double bond by catalytic hydrogenation according to methods described within the literature. 
Diester of structure 2 can be prepared from the ester 1 by alkylation with t-butyl bromoacetate in the presence of a base, such as lithium diisopropylamide, in a solvent such as THF. The diester 2 can be selectively converted to the monoester 3 by saponification with an aqueous base, preferably lithium hydroxide. The acid 3 can be reduced to the alcohol 4 according to published literature procedures. The alcohol 4 can be converted to the azide 5 via a 2-step procedure involving first conversion of the alcohol into its tosylate or mesylate and then followed by treatment with excess sodium azide. The azide 5 can be converted to the GABA analog by another 2-step reaction sequence. Reduction of the azide group to an amine and then deprotection of the t-butyl ester to the acid 8 produced the desired GABA analog. Alternatively, the t-butyl ester can be deprotected first before the reduction of the azide. The sequence of reaction also gave the required amino acids. 
The GABA analogs of the current invention can be prepared enantioselectively by substituting the racemic acid 3 with the corresponding chiral acid. The chiral acid 3 was prepared as shown in Method B where the acid 9 is coupled with any of the Evans"" chiral oxazolidinones to give compound 10. Compound 10 was alkylated with t-butyl bromoacetate in the presence of a base, such as lithium diisopropylamide, in a solvent such as THF to give the chiral ester 11. The ester 11 was saponified to the chiral acid 3 by lithium hydroxide and hydrogen peroxide treatment. The chiral acid 3 was converted to the chiral GABA analogs using the same reaction sequence as shown in Method A. 
Method C can be used to prepare some of the GABA analogs of generic structure II in the current invention. The key intermediate 15 can be prepared from compound 12 via a 3-step Michael addition, Boc deprotection and reduction sequence. The amino lactam 15 can be reacted with an appropriately substituted carbonyl compound in the presence of an acid, preferably acetic acid to give the pyrrole derivative 16. Reprotection of the lactam 16 as its Boc analog followed by lithium hydroxide saponification will give the acid 18. The Boc protecting group can be removed by acid treatment to give the desired GABA analog 19. 
The acid 22 can be prepared by treating the amino acid 20 with an appropriately substituted carbonyl compound 21 in the presence of an acid, preferably acetic acid. The ester 23 can be prepared by heating to reflux of the corresponding acid in a solvent such as ethanol and the like in the presence of a catalytic amount of mineral acid such as hydrochloric acid. It can also be prepared from the acid with an appropriate chloroformate in the presence of DMAP and a base such as triethylamine according to methods described within the literature. Diester of structure 24 can be prepared from the ester 23 by alkylation with t-butyl bromoacetate in the presence of a base, such as lithium disopropylamide, in a solvent such as THF. The diester 24 can be selectively converted to the monoester 25 by saponification with an aqueous base, preferably lithium hydroxide. The acid 25 can be reduced to the alcohol 26 according to published literature procedures. The alcohol 26 can be converted to the azide 27 via a 2-step procedure involving first conversion of the alcohol into its tosylate or mesylate and then followed by treatment with excess sodium azide. The azide 27 can be converted to the GABA analog by another 2-step reaction sequence. Reduction of the azide group to an amine and then deprotection of the t-butyl ester to the acid 29 produced the desired GABA analog. 
The GABA analogs of generic structure II in the current invention can be prepared enantioselectively by substituting the racemic acid 25 with the corresponding chiral acid. The chiral acid 3 was prepared as shown in Method E where the acid 22 is coupled with any of the Evans"" chiral oxazolidinones to give compound 30. Compound 30 was alkylated with t-butyl bromoacetate in the presence of a base, such as lithium diisopropylamide, in a solvent such as THF to give the chiral ester 31. The ester 31 was saponified to the chiral acid 25 by lithium hydroxide and hydrogen peroxide treatment. The chiral acid 25 was converted to the chiral GABA analogs using the same reaction sequence as shown in Method D.